grimshaw



1959 c. s. GR|MSHAW 2,899,801

AUTOMATIC DEFROSTING- EVAPORATOR ARRANGEMENT Filed June 25. 1956 INVENTOR. CHARLES s. GRIMSHAW H is ATTORNEY United States Patent 0.

AUTOMATIC DEFROSTING EVAPORATOR GEMENT Application June 25, 1956, Serial No. 593,618

3 Claims. (Cl. 62--156) The present invention relates to an automatic evaporator defrosting arrangement and is more particularly concerned with an evaporator and defrost control arrangement adapted to assure complete defrosting of the evaporator during each idle period of the refrigerating system.

During the operation of a household refrigerator, moisture from the air within the refrigerated compartment or compartments collects on the evaporator surfaces in the form of frost when these surfaces are below freezing and if this frost layer is allowed to remain on the surfaces it will decrease the efliciency of the refrigerating unit. In order to avoid the necessity for manually defrosting the evaporator surfaces, various schemes have been proposed and used to obtain the automatic defrosting thereof. A simple arrangement for defrosting an evaporator serving only a fresh food storage compartment comprises operating the evaporator within a range of temperatures such that during the idle or oil? period of the refrigerating unit, the evaporator rises to a temperature sufiiciently high to effect melting of all the frost that has collected thereon during the operating period of the unit. For the successful operation of such defrosting scheme, it is essential that the entire evaporator structure come up to defrosting temperatures during each idle period. Otherwise there will be experienced a continual accumulation of ice on those portions of the evaporator which are not completely'defrosted and this accumulation will eventually interfere with the desired operation of the refrigerator, or at the very least be a source of annoyance to the user. For that reason in the use of this type of defrosting scheme, it has been found necessary to provide heaters in contact with certain portions of the evaporator, as for example the inlet or outlet to make certain that these portions slow to defrost will be brought up to defrosting temperatures before the unit is again energized. Such heaters have of course been energized during the unit oif? cycle and de-energized during the on cycle.

It is a-n object of the present invention to provide a refrigerator including a storage compartment, a refrigerating system including an evaporator for cooling the compartment and means responsive to the temperature of the evaporator for assuring complete defrosting of the entire evaporator during each off cycle of the system.

Another object of the invention is to provide an improved construction and arrangement of an evaporator and the control means for preventing energization of a refrigerating system until the temperature of the entire evaporator has reached a defrosting point.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In carrying out the objects of the present invention, there is provided a refrigerator comprising a fresh food storage compartment, an evaporator disposed in that compartment and a condensing unit for supplying refrig- 2,899,801 Patented Aug. 18, 1959 erant to the evaporator. Means connecting the condensing unit to the evaporator include an inlet tube connected to the evaporator for supplying condensed refrigerant thereto and an outlet tube connected to the evaporator for withdrawing refrigerant from the evaporator. The operation of the condensing unit is under control of an electrical control system including a vapor-filled feeler bulb and the control is adapted to energize the unit only when the feeler bulb senses temperatures above freezing. In order to assure complete defrosting of the evaporator during each idle period, the feeler bulb is arranged in thermal contact with both the inlet and outlet tubes at a point within the storage compartment. By this arrangement in which the feeler bulb senses both the inlet and outlet temperatures of the evaportor and is responsive only to the colder of the two, there is assured complete defrosting of the entire evaporator during an idle period and before the condensing unit is again energized. For a better understanding of the invention, reference may be had to the accompanying drawing in which:

Fig. 1 is a front elevation view of a portion of a refrigerator incorporating an embodiment of the present invention; and

Fig. 2 is a schematic showing of a refrigerating systemv and a condenser 8. The system further includes a rear wardly sloping fresh food storage compartment evaporator 9 which is disposed. within the storage compartment 3 for cooling this compartment and a low temperature or freezer evaporator 10 for maintaining the freezer com partment 2 at below freezing temperatures. The freezer evaporator 10 comprises tubing arranged in closed loop of generally serpentine form and secured, iu-a manner well known in the art, to the walls of the freezer com partment 2.

Condensed or liquid refrigerant is supplied from th condenser 8 through a capillary tubell to the lower rear,

pass 9a of the storage compartment evaporator 9 through an inlet tube 12 at the lower rear side of the evaporator, a portion of which as shown in Fig. 1 is disposed within the storage compartment 3. Refrigerant from the evaporator 9 passes through an outlet tube 13, a portion of which is also disposed within the storage compartment 3, to the freezer evaporator 10 through a trap 14 to prevent reverse flow of refrigerant from the freezer evaporator to the fresh food evaporator. The refrigerant conducted to the evaporatorlll is preferably introduced through an injector 15, one function of which is to promote the circulation of refrigerant through the closed or flooded evaporator 10 which includes in addition to the serpentine tubing 16 a header 17. Vaporized refrigerant is returned to the condensing unit from the header 17 of the freezer evaporator 10 through a suction line 18.

The operation of the condensing unit 6 is controlled by a switch 19 adapted to engage the contacts 20 in a line 21 through which power is supplied to the motor compressor unit 7. Means for actuating the switch 19 comprises a bellows 22 connected by means of a tube 23 to a feeler bulb 24 responsive to the temperature of the storage compartment evaporator 9. The control system including the switch 19 is so constructed that the motor compressor unit 7 is energized whenever the vapor-filled feeler bulb 24 does not sense any temperature below freezing, that is, below defrosting temperatures. Once the motor compressor unit 7 is energized, the refrigerating system continues to operate until the feeler bulb senses a predetermined low temperature. In a two-temperature refrigerator, such as that illustrated, where it is desirable to maintain the freezing compartment at substantially F., this low temperature at which the motor compressor unit 7 is de-energized, is generally in the neighborhood of or below 0 F. By this arrangement the freezer compartment 2 is continuously held at sub freezing temperatures while the storage compartment 3 is maintained at a somewhat higher temperature which will not freeze the contents thereof but which will nevertheless preserve the contents of the compartment 3 over a reasonable period of time.

During each operating cycle of the condensing unit 6, moisture in the air contained within the storage compartment 3 condenses on the storage compartment evaporator 9 in the form of frost. As this frost collects over the entire surface area of the evaporator 9 which is preferably in the form of a continuous conduit or tube of serpentine configuration as shown in the drawing, the melting thereof requires that the entire evaporator be allowed to attain a temperature above freezing, that is, a defrosting temperature, during the subsequent ofi cycle.

In order to assure this result, the feeler bulb 24, in accordance with the present invention, is positioned in heat exchange relationship with both the inlet 12 and the outlet 13 of the evaporator 9 immediately adjacent the point 27 where these tubes enter the storage compartment 3. As the feeler bulb 24 is partially filled with a volatile liquid or in other words is part of what is known as a vapor-filled thermostat, it is responsive only to the coldest temperature sensed thereby. In other words the switch 19 will be closed by expansion of the bellows 22 only when all of the temperatures sensed by the feeler bulb 24 are above freezing. Thus by placing the feeler bulb 24 in contact with both the inlet and the outlet tubes of the evaporator 9, the energization of the motor compressor 7 is delayed until such time as both the inlet 12 and outlet 13 of the evaporator 9 have attained defrosting temperatures thus assuring that all points between the inlet and outlet or in other words the entire evaporator 9 has also reached a defrosting temperature.

The evaporator and control arrangement of the present invention is particularly useful in defrosting the fresh food compartment evaporator of two-temperature refrigerating systems such as that shown in the drawing in which there is no substantial restriction or pressure differential between the storage compartment evaporator 9 and the freezer compartment evaporator 16. With a system in which there is no substantial pressure difierential between the two evaporators and hence no substantial temperature differential, it is necessary to continue the operation of the motor compressor 7 during each on cycle until both evaporators have attained a temperature sufficiently low to maintain the freezer compartment 2 at subsantially 0 F. In oher words both the evaporator 9 and the evaporator 16 operate at substantially the same I pressures and temperatures and must be brought to this low temperature. Therefore during the subsequent ofi cycle, it is necessary for the evaporator 9, which is gradually warmed by the air within the storage compartment 3, to experience a temperature change from about 0 F. to a temperature a few degrees above freezing in order to assure complete defrosting thereof. It has been found that by positioning the control or feeler bulb 24 in contact with both the inlet 12 and the outlet 13 of the evaporator 9 rather than in contact with only one of these tubes or with some other point on the evaporator intermediate the inlet and outlet, complete defrosting of the entire evaporator is assured during each off cycle without the use of heaters or the like for selectively warming certain sections of the evaporator.

While there has been shown and described a specific embodiment of the invention it is not desired that the invention be limited to the particular construction shown and described and it is intended by the appended claims to cover all such modifications within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A refrigerator comprising a cabinet including a freezer compartment and a fresh food storage compare ment, an evaporator disposed in each of said compartments, a condensing unit, means connecting said unit and evaporator-s in closed series connection and including an inlet tube connected to the evaporator in said storage compartment for supplying refrigerant to said evaporator and an outlet tube connected to said storage compartment evaporator for withdrawing refrigerant therefrom, temperature-responsive means including a feeler bulb partially filled with a volatile liquid for controlling the operation of said condensing unit and adapted to energize said unit only when all temperatures sensed by said feeler bulb are above freezing, said feeler bulb being disposed in said storage compartment in thermal contact with beth said inlet and outlet tubes within said storage compartment to assure complete defrosting of said-storage compartment evaporator prior to energization of said can'- densing unit.

2. The refrigerator of claim 1 in which said outlet tube connects said storage compartment evaporator to the freezer compartment evaporator.

3. The refrigerator of claim 2 in which said-storage compartment evaporator comprises a continuous length of tubing of serpentine configuration.

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